A prominent society has launched its public fight against the latest plans for Hampstead Heath’s dams – saying they pose the greatest threat to the park since the 1800s and risk “permanently disfiguring” the landscape.

The Heath and Hampstead Society says this City of London artist's impression fails to show the true impact of raising the dam

The Heath and Hampstead Society – founded in 1897 with a mission of safeguarding the Heath – has heavily criticised new proposals presented by the City of London Corporation and threatened to seek legal action if they cannot be halted.

The society is now rallying opposition and has urged residents to get behind the organisation at a public meeting on November 25 – the day before the Corporation launches a three-month consultation.

The society has long been quietly critical of the £15million project to protect against flooding proposed by the City, which manages the Heath.

But now it has gone public for the first time with grave doubts about the shortlisted proposals unveiled earlier this month, after Heath bosses had pledged to scale back works earlier this year.

In the society’s latest newsletter, which went out this week, chairman Tony Hillier writes: “We are deeply concerned at the direction being taken by the City.

“We believe these proposals are a much greater threat to the Heath landscape today than the works proposed by the LCC in 1895 that brought the society into being.

“We urge the City and their advisers to stop ignoring a whole series of reasons why they can still soften the designs to make them more appropriate for this very special landscape.”

In 1895, London County Council provoked national outcry with plans to turn the Heath into a municipal park, removing much of its wild nature.

Mr Hillier added that, while the latest designs are an improvement compared with earlier options, they will still “permanently disfigure the Heath in a way which is not necessary”.

The greatest fears centre on the raising of a dam between the Model Boating Pond and the Highgate Men’s Bathing Pond by between two and 2.5 metres.

The society argues that such drastic measures – which would destroy views from the pathway between the two ponds – are being driven by a deeply misguided legal approach.

The Corporation says the work is mandated by UK reservoir laws, to protect against potential deaths in downstream areas like Gospel Oak in the event of extreme floods, which it acknowledges are highly unlikely.

But Mr Hillier insisted the City is failing to properly take into account its statutory requirement to protect the Heath’s “unique wild and natural qualities”, which means that only the “minimum legally necessary” should be done.

He urged the City to take a “more balanced interpretation of the law” and said the society “may consider mounting a formal challenge” if the plans remain “unacceptable”.

A spokesman for the City of London said: “The City Corporation as a responsible public body and owner of the Heath has no choice, following the advice of independent dam engineers, but to carry out work to strengthen some dams on Hampstead Heath, thereby protecting the local community who live downstream of the Heath from potential dam failure in extreme rainfall events.

“The City’s design team have presented their preferred options for each chain of ponds that achieve the best solution for the Heath whilst meeting the industry guidance in ‘virtually eliminating’ the risk of future dam failure.

“A public consultation exercise will take place from the end of November until mid-February when the City aims to reach as many people as possible to gather views on the different preferred options.”

The public meeting is at St Stephen’s in Rosslyn Hill, Hampstead, at 8pm on November 25.

A controversial proposal to build an 11-storey residential tower in the heart of West Hampstead will be considered by Camden Council tonight – as the lone Labour councillor vocally opposing the plans is criticised by colleagues and branded “misguided”.